Have you used LW before & not had a problem with download speed?
Check out the thread below (the first few posts by murasame) for tips about how to optimise your LW's performance.
A few things to consider while configuring Limewire for optimal performance...
Download a file from here & see what kind of speed you get.
Magnetmix
If that magnetmix file downloads slowly as well, it can point to an ISP shaping p2p bandwidth. Please give us your system details.
System details - help us to help you -> Provide these details when you post!!!(click on link)